Hardener for water glass cements



I J 1 May 20, 1969 HLQCH ET AL 3,445,257

HARDENER FOR WATER GLASS CEMENTS Filed May 18, 1965 Sheet of 2 FIG.

MOGRA v/MUR/c ANALYSIS TL or HEAT/N6 4-.7'c./M/M

FFERE/VT/AL THERMAL ANAL YS/S P2 0 Al203 =2.5",

475 OF HE'AT/NG i fO'C./M/IV.

ENDOTHERM/C AT EXOT/IERM/C TEMP. '6'.

May 20, 1969 HLOCH ET AL 3,445,257

HARDENER FOR WATER GLASS CEMENTS Filed May 18, 1965 Sheet 2 of 2 RATE OF A/YO/POLYS/S 47 017 l0-ll WEIGHT 0F SAMPLE /.00

GRAIN SIZE 0250mm.

ml. 0.25 Na 0 MINUTES United States Patent Int. Cl. C09c 1/6431/40; C08k N82 US. Cl. 106-84 3 Claims ABSTRACT OF THE DISCLOSURE An improved process has been provided for hardening water glass cements which comprises employing as a hardener a condensed aluminum phosphate prepared by subjecting acid aluminum phosphate consisting essentially of P 0 and A1 0 in a ratio within the range of 1.1 to 3 to a two-stage thermal treatment during the first stage of which, the acid aluminum phosphate is heated to a temperature of less than about 400 C. until the weight of said acid aluminum phosphate remains constant and during the second stage of which, the acid aluminum phosphate is heated to a temperature of less than about 750 C. until the weight of said acid aluminum phosphate remains constant.

The present invention provides a hardener for water glass cements.

In the construction of chemical apparatus and furnaces cement masses containing water glass as a binder have found a wide use. These cement masses are formed of a filler that is resistant to acids or to high temperatures, for example, quartz sand, barium sulphate or chamotte, an alkali silicate, for example, potash water glass, and a hardener which brjpgwahout the hardening of the cement massesby the separation of silica gl W "Up to now alliali'silicoiluorrdes have been the most often used hardeners. However, these have considerable disadvantages. Under the action of an acid, these silicofluorides give off hydrogen fluoride whereby the liquids which come into contact with the linings of the apparatus are contaminated and, moreover, not only metals but also the mineral linings themselves are corroded.

The alkali and the fluorine introduced by the alkali silicofluorides reduce the resistance to high temperatures of refractory cements which contain predominantly chamottes as fillers.

It has been proposed to eliminate these disadvantages by replacing the silicofluoride used as a hardener by an organic hardener, especially by an amide or an ester of a fatty acid of low molecular weight. Products of this kind, too, have been used without satisfying, however, all the requirements.

It has also been proposed to use stoichiometrically acid phosphates which do not have an alkaline reaction as hardeners for water glass cements. However, these phosphates are not widely used in practice because the cement masses prepared for use do not have a sufiicient pot life.

Now we have found that the aforesaid disadvantages can be avoided by using as a hardener for water glass cements a condensed aluminium phosphate obtained by subjecting'an acid aluminum phosphate containing P 0 and A1 0 in a ratio within the range of 1.1 to 3, preferably 2 to 3, to a thermal treatment in the first stage of which the compound is heated to at most 400 C. until its weight remains constant and in the second stage of ice which the compound is heated to at most 700 C., again until its weight remains constant.

Water glass cements which, according to the invention, contain a condensed aluminium phosphate as a hardener are waterproof immediately after hardening whereas the water glass cements which are hardened by means of alkali silicofluoride or organic hardeners become waterproof after repeated acidification only. The use of the condensed aluminium phosphates according to the invention as hardeners also brings about a considerable increase of the resistance of the cements to mineral acids. Besides, the attack of strong mineral acids does not lead to the splitting off of detrimental or aggressive substances as is the case when silicofluorides are used.

The cements may be prepared from potash or soda water glasses in which the ratio of SiO,, to Me O may vary within wide limits, for example, within the range of about 1.5 to 4.0. The higher the concentration of the water glasses the higher the strength of the cements obtained. In general it is advantageous that the cements contain 25 to 30 parts of water glass and 90 to 100 parts of filler per 4 parts of hardener. Suitable fillers are the materials that are generally used for this purpose, for example, silicon dioxide in its various crystallographic forms such as guartz or christobalit, aluminium silicates such as kaolin and c l ays, silicon carbides or heavy spar. Which fillef'o'f mixture of fillers is to be used depends on the purpose for which the water glass cements are to be used.

The condensed aluminium phosphates used as hardeners for water glass cements according to the invention are prepared from aluminium ortho phosphates which contain P 0 and A1 0 in a ratio within the range of 1.1 to 3 and which are prepared in known manner, for example, by introducing the hydrate of alumina or alumina gel into phosphoric acid, evaporating resulting solution and drying the phosphate obtained. According to the invention the aluminium ortho phosphates are subjected to a stepwise thermal treatment. They are first heated to at most 400 C. until their weight remains constant and then to at most 750 C., likewise until their weight remains constant. The lower limit of the range of temperature at which the phosphates are treated is at about 200 C. and depends on the composition of the aluminium ortho phosphate used. It can easily be determined by a thermogravimetric or differential thermal analysis.

In the first stage of the thermal treatment the temperature must not exceed 400 C. before the weight remains constant. For if the condensation is carried out by heating the phosphates directly to a temperature above 400 C., that is to say by eliminating the first stage of the thermal treatment, the compounds obtained cannot be used as hardeners.

The thermal treatment may be carried out batchwise or continuously, for example, in a rotary tubular furnace.

Some values relating to the thermal treatment are illustrated by the curves shown in FIGURES 1 and 2 of the accompanying drawings. The curve shown in FIG- URE l is based on the values obtained by the thermogravimetric analysis and the curve shown in FIGURE 2 is based on the values obtained by the differential-thermal analysis. In either of the curves reference numerals 1 and 2 point to the changes in the course of the curves which are due to a loss of weight brought about by the elimination of water and which are characterized by an endothermic reaction. The above examinations were carried out with an aluminium ortho phosphate containing P 0 and A1 0 in a ratio of 2.5.

The following examples which are not intended to limit the invention serve to illustrate the preparation of the hardener for water class cements according to the mvention.

3 EXAMPLE 1 320 grams of the hydrate of alumina containing 64 to 65% of A1 were suspended in 250 cc. of water. The resulting suspension was slowly introduced, while stirring, into 1300 grams of preheated phosphoric acid containing 55% of P 0 whereby the hydrate of alumina was dis solved with the evolution of heat. The clear solution which formed was evaporated until it began to become turbid. The removal of water was continued by heating the solution for 48 hours to a temperature within the range of 170 to 200 C. It would also have been possible to carry out the drying in a spray drier or a drum drier. The dried product was ground into coarse particles and then first heated for 2% hours to a temperature within the range of 350 to 450 C., on an average to a temperature of about 400 C., and then for another 2% hours to a temperature within the range of 500 to 600 C., on an average to about 550 C. After having been cooled the finished hardener was finely ground.

EXAMPLE 2 This example is to demonstrate that the thermal treatment can also be carried out by means of a continuously operating apparatus, for example, a rotary tubular furnace.

18.2 kg. of the hydrate of alumina containing 64% of A1 0 were suspended in about 25 litres of water and introduced in small portions, while stirring continuously, into 74 kg. of phosphoric acid which contained 55% of P 0 and which had been preheated to about 90 to 100 C. The resulting solution which had a temperature of about 80 to 90 C. was freed from water in a spray drie'r, the through-put being 7 to 9 litres per hour. 550

to 600 cubic metres (measured at N.T.P.) per hour of air at 210 to 260 C. were introduced into the drier. At the place where the air entered the apparatus the temperature was within the range of 180 to 220 C. By operating in this manner about 62 kg. of a crystalline product having a total content of water of 16% (crystal water and chemically bound water, determined by the loss on heating at 800 C.). The product was further dried at a temperature within the range of 220 to 260 C. until the content of water (determined by the loss on heating) was within the range of 6 to 8%. (This drying operation can be carried out, for example, in a shelf drier, a truck drier, a belt-type drier or a rotary drum drier.) During this operation a slight sintering set in. Subsequently the thermal treatment was carried out in a rotary tubular furnace having a length of 1.5 metres.

3.5 to 4 kg. of material were put through per hour. About 1 kg. of material was always present in the furnace. The heating was adjusted in such a manner that approximately the following temperatures prevailed in the different parts of the furnace:

First third of the furnace: 300 to 400 C.; Second third of the furnace: 400 to 500 C.; and Outlet of the furnace: 600.

The products obtained by the experiments described in Examples 1 and 2 had the following composition:

77.2 of P205, 22.4% of A1 0 0.4% loss on heating.

The products were not hygroscopic and when stored their hardening properties were not impaired.

As can be seen from FIG. 3, the curve representing the hydrolysis of the condensed aluminium phosphate obtained according to Examples 1 and 2 and a pH of 10 to 11 is nearly linear for the first 30 minutes. For the purpose of determining the rate of hydrolysis 1 gram of the product was suspended in water and the resulting 4 suspension was adjusted to a pH of 10 to 11 by means of sodium hydroxide solution. The said pH value was maintained 'by the automatic addition of 0.25 N-sodium hydroxide solution. FIG. 3 demonstrates the addition of 0.25 N-sodium hydroxide solution as a function of time.

EXAMPLE 3 A hardener containing P 0 and A1 0 in a ratio of 3 was prepared in the manner described in Example 1 but instead of the hydrate of alumina the equivalent amount of an alumina gel of the formula Al (OH) Cl was used for the preparation of the aluminium ortho phosphate.

With the use of the aluminum phosphate prepared according to Examples 1 and 2 a water glass cement was prepared in the following way:

96 parts by weight of a quartz sand containing 3% of particles having a diameter of more than 0.15 mm., 61% of particles having a diameter within the range of 0.15 to 0.125 mm. and 36% of particles having a diameter of less than 0.125 mm. were intimately mixed with 4 parts by weighfoThardener. 30 parts by weight of h water lass containing K 0 and SiO in a ratio of 1:1.88 and having a density of 1.42 were added and the mixture was stirred well. The resulting cement had a pot life of 30 minutes and then hardened within 24 hours, forming a mass that was resistant to acids and water.

The following Table I collates the mechanical and chemical properties of the cement prepared with a hardener according to the invention and those of commercially available cements which had been hardened by means of an amide of an organic acid and a silicofluoride, respectively.

TABLE I Cement containing Commercially the hardener available according to cement the invention Compressive strength after a storage of 8 days:

In the air 186 kg./cm. L... 310 kgJemJ In water Destroyed 240 kgJcm. in H2804 0t 96% strength ..do. 280 kg./cm.' Adhesion to iron after a storage of 8 day in the air 15 kgJcm. 19 kg./em. Adhesion to ceramic stone immediately after hardening, in the air 30 kgJem. 25 kgJcm. In H2504 or 96% strength:

Alter 8 days Adhesion lost... 14 kgJem. After 4 weeks ..do

l Containing an organic hardener. 9 Containing silicofluoride as a hardener.

A B 0 K20 14. 5% NazO 7.5% K20 11.2%

sto, 27. 27 25. 5'7 .57 Density 1.42" 1. a5 1. e5 SlOz/MezO 1.88 2. 2 Viscosity at 20 C 50 e1 38 c1 45 c1 As can be seen from the following Table II the cements prepared with the use of the hardener according to the invention were resistant to water without having been subjected to an aftertreatment whereas the cement containing an organic hardener was waterproof only after having been acidified several times after hardening. The latter 'of which, the acid aluminum phosphate is heated to a also applies to cements containing an alkali silicofluoride temperature of less than about 750 C. until the weight as a hardener. of said acid aluminum phosphate remains constant.

TABLE II Cement powder Cement powder containing a hardener according to containing a Examples 1 and 2 (P205:AlzO =2-5) hardener according to Example 3 (P2Os:A1zOs=3) Commercially (95 g. of a sand available acidmixture, 5 g. of 100 g. of cement 100 g. of cement 100 g. of cement proof cement hardener), 100 g. powder (96 g. of powder (96 g. of powder (97 g. of containing an of cement a sand mixture, a sand mixture, a sand mixture, organic hardener: powder, 25 g. of 4 g. of hardener), 4 g. of hardener), 3 g. of hardener), 100 g. of cement water glass A, 28 g. of water 27 g. of water 27 g. of water powder, 36 g. of pot life 45 glassA, pot life glass B, pot life glass 0, pot life water glass A, minutes, period 50 mms., period 50 mins., period 50 mins., period Test specimen having the form of a cylinder of pot life 45 of hardening 24 of hardening 24 of hardening 24 of hardening 24 25 mm. x 25 mm. minutes hours hours hours hours Compressive strength in the cold after a storage in the air of- 8 days 175 kgJcmJ. 258 kgl/cm 2 157 kgJcm. 138 kgJem. 105 kgJemJ. 4 weeks 250 kg./em.= 340 kg./cm. 336 kgJcm. 250 kg./cm. 200 kg./cm..

Adhesion to iron (measured as tensile strength in the cold) alter a storage in the air of- 8 days 12.4 kg.lcm. 17.9 kgJcmfi 14.1 kg.lcm. 4 weeks kgJcm. 24 kgJcm. 13.9 kgJcm. Adhesion to ceramic stone (measured as tensile strength in the cold) after a storage in the air- 12.1 kgJcm. 12.1 kgJcmJ.

0t 8 days kgJcm. 23.6 kg./cm. 7 kgJcm. 15 16.5 kg./cm. Of 4 weeks kgJcm. 30 kg./cm. kgJcm. kgJcm. 14.8 kg./cm. Of 14 days, ageing for 16 hours at 90 C. and 10 kgJcm. 20 kgJem. 14. kg.lem. 13. kg./cm 3.8 kgJcmJ.

subsequent storage [or 6 weeks in H2804 of 70% strength, at 20 C. Of 14 days and subsequent storage for 6 Destroyed ..do 14.4 kgJcm. 14.0 kg./cm. 6.4 kg./cm.

weeks in H2804 of 70% strength.

Compressive strength in the cold of the test .....de 205 kgJcm. 141 kgJcm. 147 kgJcm. 114 kgJcmJ.

specimens after a. storage of 8 days and subsequent boiling in drinking water for 8 hours.

What we claim is: 2. In the process for hardening water glass cement I 1. In the process for hardening a water glass cement according to claim 1 wherein the acid aluminum phoscomprising water glass and filler to which is added and phate consists essentially of P O :Al O within the range admixed a hardener therefor and the mixture is hardened, of 2 to 3.

wherein the improvement comprises adding as a hardener 3. In the process for hardening water glass cement to the cement to harden the same in a ratio of about according to claim 1 wherein the acid aluminum phos- 6.2 to 7.5 :1 water glass to hardener a condensed alumiphate i an l i orthophosphate having a p 0 and num phosphate prepared by subjecting acid aluminum 1 0 ratio f 2 5 phosphate consisting essentially of P 0 and A1 0 in a References Cited ratio within the range of 1.1 to 3 to a two-stage thermal treatment during the first stage of which, the acid FOREIGN PATENTS aluminum phosphate is heated to a temperature of less 449,983 7/ 1948 Canada. than about 400 C. until the weight of said acid aluminum phosphate remains constant and during the second stage JAMES E. POER, Primary Examiner. 

